Multistatic fiber-based system for measuring the Mueller matrix bidirectional reflectance distribution function

Authors: SCARBORO, CLIFTON - North Carolina State University; DOHERTY, COLLEEN - North Carolina State University; Balint-Kurti, Peter; KUDENOV, MICHAEL - North Carolina State University

Submitted to: Applied Optics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/20/2022
Publication Date: 11/20/2022
Citation: Scarboro, C.G., Doherty, C.J., Balint Kurti, P.J., Kudenov, M.W. 2022. Multistatic fiber-based system for measuring the Mueller matrix bidirectional reflectance distribution function. Applied Optics. 61(33):9832-9842. https://doi.org/10.1364/AO.470608.
DOI: https://doi.org/10.1364/AO.470608

Interpretive Summary: Non-uniform reflections of light from a leaf can be a significant confounding factor when attempting to correlate hyperspectral remote sensing data with certain phenotypes, such as chlorophyll or water content, that characterize plants’ interaction with their environment. The bidirectional reflectance distribution function (BRDF) is effectively used to characterize the reflectivity of surfaces over all light source and viewing positions, and correct remote sensing measurements. However, measuring BRDFs in a laboratory setting can be time consuming, especially when collecting polarized (light wave orientation) BRDF measurements of an object by conventional goniometric techniques, where a light source and detector sweep across many geometries relative to a target. We present a system for collecting polarized BRDF measurements using optical fibers that are fixed in place around an object and are also coupled to a series of detector arrays. Each fiber is mounted on a steel hemisphere at a known angular position relative to the center point. Furthermore, the fibers are randomly located around the hemisphere, and the entrance to each fiber contains a particular polarization element (e.g. linear polarizer, waveplate). This allows simultaneous acquisition of polarized reflection intensities at many viewing positions. A white LED source illuminates the target surface with a onfigurable polarization state and is mounted on a rotating arm that sets its angle. We describe the setup, calibration, and data processing for this system and present its performance as applied to measurements of a 600 grit ground glass diffuser.

Technical Abstract: Bidirectionality effects can be a significant confounding factor when measuring hyperspectral reflectance data. The bidirectional reflectance distribution function (BRDF) can effectively characterize the reflectivity of surfaces to correct remote sensing measurements. However, measuring BRDFs can be time-consuming, especially when collectingMueller matrix BRDF (mmBRDF) measurements of a surface via conventional goniometric techniques. In this paper, we present a system for collecting mmBRDF measurements using static optical fiber detectors that sample the hemisphere surrounding an object. The entrance to each fiber contains a polarization state analyzer configuration, allowing for the simultaneous acquisition of the Stokes vector intensity components at many altitudinal and azimuthal viewing positions.We describe the setup, calibration, and data processing used for this system and present its performance as applied to mmBRDF measurements of a ground glass diffuser.